1. Field of the Invention
The present invention relates to a light-emitting element using Group III nitride compound semiconductors for optical communication. For example, the intention can be applied to an optical transmitter of a communication system using a plastic optical fiber (POF).
2. Description of the Related Art
A system using a light-emitting diode (hereinafter simply referred to as “LED”) as a light source for a short-distance LAN using a plastic optical fiber (POF) has been known recently. In the system, a red LED using a GaAs compound semiconductor is used as a light-emitting element for optical communication. Short-distance communication using an LED has been examined and developed eagerly. The high cutoff frequency of the red LED is 30 MHz.
The transmission loss of the POF is low in a short wavelength range, for example, in an emission wavelength range of from 450 nm to 550 nm. Accordingly, for optical communication using the POF, use of a light-emitting element such as an LED emitting light in an emission wavelength range of from 450 nm to 550 nm is preferred to use of the red LED. It is therefore conceived that a light-emitting element using a Group III nitride compound semiconductor is used as a light source for optical communication.
When an existing Group III nitride compound semiconductor light-emitting element is used, there is however a problem that the response rate is low. Firstly, there is a problem that light-emitting characteristic deteriorates as current density increases, that is, luminance is saturated relative to current. Further, for example, a p-layer or a p-electrode on the p-type layer needs to be small-sized in order to reduce a capacitance component formed by a light-emitting layer to improve the response rate. It is however difficult to perform bonding if the size of the p-layer or p-electrode is too small.